"Backpacking".Full Description.Mission Specialist Bruce McCandless II ventured further away from the confines and safety of his ship than any previous astronaut ever has. This space first was made possible by the Manned Manuevering Unit or MMU, a nitrogen jet propelled backpack. After a series of test maneuvers inside and above Challenger's payload bay, McCandless went "free-flying" to a distance of 320 feet away from the Orbiter. The MMU is controled by joy sticks positioned at the end of the arm rests. Moving the joy sticks left or right or by pulling them fires nitrogen jet thrusters propelling McCandless in any direction he chooses. A still camera is mounted on the upper right portion of the MMU. This stunning view shows McCandless with the MMU out there amongst the black and blue of Earth and space. Photographer: NASA